More distant old firm supported by former monarch (5)
I believe the answer is:
icier
'more distant' is the definition.
(icy can mean distant)
'old firm supported by former monarch' is the wordplay.
'old firm' becomes 'ici' (former company Imperial Chemical Industries).
'supported by' is a charade indicator (letters next to each other) (in a down clue, some letters hold up others).
'former monarch' becomes 'ER' (Elizabeth Regina, ie Queen Elizabeth).
'ici'+'er'='ICIER'
(Other definitions for icier that I've seen before include "rather cold" , "More chilly" , "More cold or frozen" , "with more reserve" , "More cold - really freezing" .)